The present invention relates to a security system, and more particularly, to a system for closing and opening a door lock of a vehicle through wireless communication with a portable device.
Japanese Laid-Open Patent Publication No. 2002-247656 describes a vehicle security system, or a smart entry device. The smart entry device includes a portable device, which is carried by a driver, and a door lock controller. The door lock controller performs wireless communication with the portable device, automatically opens the door locks of a vehicle when the driver approaches the vehicle, and automatically closes the door locks when the driver moves away from the vehicle.
FIG. 15 shows a prior art portable device 80. A case 81 accommodates a battery and electric components (not shown). Further, the case 81 includes a transponder 82, which is used in an emergency state such as when the battery voltage decreases, and a mechanical key 83, which is retained in a key retainer 84. If the portable device 80 cannot perform wireless communication when the voltage of the battery decreases, the driver removes the mechanical key 83 from the key retainer 84, uses the mechanical key 83, and mechanically opens and closes the door locks.
Since the door locks are normally opened and closed through wireless communication with the portable device 80, the mechanical key 83 is seldom used. Thus, the driver may keep carrying the portable device 80 without noticing that he or she has lost the mechanical key 83 or forgotten to return the mechanical key 83 to the key retainer 84. In such a case, if wireless communication with the portable device 80 is disabled when the voltage of the battery decreases and the mechanical key 83 is not retained in the portable device 80, the driver cannot open or close the door locks. This would be inconvenient since the driver would not be able to enter the vehicle.